1. Field of the Invention
The present invention relates generally to a combination lock for storably holding various items. More particularly, the present invention relates to a combination lock which assures that unlocking can easily be achieved with substantial reduction of rotation of dial plates.
2. Description of the Prior Art
To facilitate understanding of the present invention, a conventional combination lock will be described below with reference to FIG. 26 to FIG. 32.
As shown in FIG. 26, a dial knob 1 includes a dial shaft 2 to a rear end of which a rear end lock plate 3a is fastened by tightening a lock nut 4 in such a manner that it is rotated together with the dial knob 1. First and second intermediate lock plates 3b and 3c and a fore lock plate 3d are rotatably fitted onto the dial shaft 2. Reference numeral 5 denotes spacers which are interposed between adjacent lock plates among the lock plates 3a, 3b, 3c and 3d, and reference numeral 6 denotes a compression spring. Unlocking cutout 7a, 7b, 7c and 7d are formed on the outer peripheries of the lock plates 3a, 3b, 3c and 3d for receiving lock pawl A when they are located in alignment with the lock pawl A so as to allow the combination lock to be unlocked. In addition, engagement projections 8 to 13 are formed on side surfaces of the lock plates in the following manner.
An engagement projection 8 is formed on the fore side surface of the lock plate 3a, an engagement projection 9 is formed on the rear side surface of the lock plate 3d, two engagement projections 10 and 11 are formed on the opposite side surfaces of the lock plate 3b and two engagement projections 12 an 13 are formed on the opposite side surfaces of the lock plate 3c. It is obvious that each of the projections 8 to 13 is formed at a predetermined position with each of the unlocking cutouts 7a to 7d as a reference position for unlocking. Reference numeral 14 denotes a plane plate fixed to an opening/closing door of a safe, and reference numerals 15 and 16 denote first and second shaft bearings of the dial shaft 2.
FIG. 27 is a perspective view which shows the lock plates 3a to 3d in the disassembled state. When unlocking is effected, first, the rear lock plate 3a is rotated in the clockwise direction by an angle of 360 degrees so that engagement projection 8 is engaged with a rear engagement projection 11 of the first intermediate lock plate 3b.
Next, as shown in FIG. 28, the lock plate 3a is rotated in the same direction by an angle of 360 degrees so that the fore engagement projection 10 of the first intermediate lock plate 3c is engaged with rear engagement projection 13 of the second intermediate lock plate 3c.
Subsequently, as shown in FIG. 29, the lock plate 3a is rotated in the same direction by an angle of 360 degrees so that the fore engagement projection 12 of the second intermediate lock plate 3c is engaged with rear engagement projection 9 of the lock plate 3d. Moreover, the lock plate 3a is rotated by an angle less than 360 degrees until a predetermined memory value (e.g., 33) is assumed. Thereafter, the unlocking cutout 7d of the lock plate 3d is kept immovable at a predetermined position where it is oriented in the upward direction.
In detail, when the rear lock plate 3a is rotated by the dial knob 1 three times, the first intermediate lock plate 3b is rotated two times and the second intermediate lock plate 3c is rotated by one revolution so that the fore lock plate 3d starts to be rotated. In addition, by rotating the rear lock plate 3a by a predetermined angle less than 360 degrees to assume a predetermined memory numeral, the unlocking cutout 7d of the fore lock plate 3d can be held at a predetermined position.
Next, as shown in FIG. 30, the rear lock plate 3a is rotated in the counterclockwise direction by an angle of 360 degrees (one revolution) so that the engagement projection 8 is engaged with rear engagement projection 11 of the first intermediate lock plate 3b. Subsequently, the rear lock plate 3a is rotated in the same direction by an angle of 360 degrees so that the fore engagement projection 10 of the first intermediate lock plate 3b is engaged with rear engagement projection 13 of the second intermediate lock plate 3c. Thereafter, the second intermediate lock plate 3c is rotated by a predetermined angle less than 360 degrees corresponding to a predetermined memory numeral (e.g., 97) so that the unlocking cutout 7c is located in alignment with the unlocking cutout 7d of the rear lock plate 3d which has been kept immovable.
Next, as shown in FIG. 31, the lock plate 3a is rotated in the clockwise direction by an angle of 360 degrees so that the engagement projection 8 is engaged with rear engagement projection 11 of the first intermediate lock plate 3b. Additionally, the first intermediate lock plate 3b is rotated by a predetermined angle less than 360 degrees until a predetermined memory numeral (e.g., 64) is assumed so that the unlocking cutout 7b is located in alignment with those of the second intermediate lock plate 3c and the rear lock plate 3d which have been kept immovable.
Finally, as shown in FIG. 32, the lock plate 3a is rotated in the counterclockwise direction by a predetermined angle less than 360 degrees until a predetermined numeral (e.g., 84) is assumed so that the unlocking cutout 7a is located in alignment with those of the first and second intermediate lock plates 3b and 3c and the rear lock plate 3d which have been kept immovable. Thus, lock pawl A is received in the unlocking cutouts 7a to 7b of the lock plates 3a to 3d, whereby the combination lock is brought to an unlocked state.
As is apparent from the above-described procedure of unlocking, a conventional combination lock is typically unlocked by rotating the knob from a reference numeral (e.g. zero) in the normal direction by three revolutions, next rotating the knob in the reverse direction to assume a predetermined memory numeral by two revolutions, further rotating the knob in the normal direction to assume to a predetermined memory numeral, finally rotating the knob in the reverse direction to reach a predetermined memory numeral.
The above procedure of unlocking is only to applicable to a combination lock comprising four lock plates, but things are same with a combination lock including three or five lock plates. For example, in the case of a combination lock including three locking plates, in accordance with the operation principle, first the dial knob is rotated from a reference numeral in the normal direction by two revolutions, next the dial knob is rotated in the reverse direction by one revolution plus a fraction corresponding to a predetermined memory numeral. Similarly, in the case of a combination lock including five locking plates, first the dial knob is rotated in the normal direction by four revolutions, next the dial knob is rotated in the reverse direction by three revolutions plus a fraction corresponding to a predetermined memory numeral, further the dial knob is rotated again in the normal direction by two revolutions plus a fraction corresponding a predetermined memory numeral, subsequently, the dial knob is rotated in the reverse direction by one revolution plus a fraction corresponding to a predetermined memory numeral. Finally, the dial knob is rotated in the normal direction to the position corresponding a predetermined memory numeral.
At any rate, with respect to the conventional combination lock, the number of revolutions of the dial knob and a plurality of memory values must be exactly memorized. For this reason, it is complicated for an unskilled user to unlock the conventional combination lock in spite of excellent locking ability thereof.
Accordingly, the conventional combination lock is not widely put into practical use.